did you ever take the panels off to see if the vac pumps move, or if you move the lever if the air flow changes? the plastic are could be broken on top of the hvac box, where the linkage leads to.
clicking could be a blend door actuator, but that only affects hot or cold air. once all the panels are off, if you hear the clicking, you can reach in and touch the actuator, you should feel it clicking if its making the sounds.